Applying hot and/or cold to sore body parts as a therapeutic treatment is well known. For example, ice packs may be applied to a sprained ankle to reduce swelling, or a container filled with hot water may be applied to a sore back to help loosen and relieve the back muscles. The potential effectiveness of a hot or cold treatment increases as the level of control for the treatment increases. In particular, the effectiveness depends on the ability to control the temperature. If cold treatments are too cold, they may cause skin and tissue damage. Similarly, if hot treatments are too hot, they may burn or otherwise damage the recipient. Therefore, systems for precisely controlling the temperature of a therapy are desirable.
Prior art devices have been developed to deliver hot or cold fluids for therapeutic purposes. For example, United States Patent Publication Number 2001/0039439 A1 to Elkins discloses a heat exchange splint and control unit with a single fluid reservoir and a mixing valve that receives a single input fluid and selectively diverts a first portion of the input fluid to a heat exchanger, while a second portion is diverted past the heat exchanger. The fluid portions recombine at a Y junction, and the temperature of the combined fluid is determined by the relative amount of fluid diverted to the heat exchanger compared to the amount of fluid bypassing the heat exchanger and flowing straight to the Y junction. The temperature of the combined fluid may be set as low as the heat exchanger permits and may achieve a maximum temperature equal to the ambient temperature of the surrounding environment.
Prior art devices have also been developed to alternately deliver hot and cold fluids for therapeutic purposes. For example, U.S. Pat. No. 6,295,819 to Mathiprakasam et al. discloses a thermoelectric heat pump fluid circuit with a single fluid reservoir and a valve that may be selectively toggled between two positions for delivering either a hot or cold fluid. The position of the valve determines which of two fluid temperatures are output by controlling the direction of fluid flow around a heat pump. When the valve is switched, the temperature of fluid in the system gradually shifts from one of two possible therapy temperatures to the other.